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    SubjectRe: [PATCH 0/8][RFC] IO latency/throughput fixes


    On Mon, 6 Apr 2009, Linus Torvalds wrote:
    >
    > Yes. I want to go back and see how much this all helps for the
    > data=ordered case (if at all), but I think we should at least consider
    > trying 'data=writeback' as a default.

    Hmm.

    So I'm back to "data=ordered", and quite frankly, so far it's a horrible
    experience.

    The difference is rather startlingly huge, which it was _not_ before.

    Sure, data=writeback was better before too, but in the end, the difference
    between the occasional 5+ second pause and the occasional 10+ second pause
    wasn't really all that interesting. They were both unusuable, and both
    made me kill the background writer almost immediately.

    This time I really forced myself to keep it around, just to get the whole
    horridness of the experience.

    Here's wahat I just got from data=writeback and all the latest patches
    (which includes one extra experimental one from Jens to further improve on
    things):

    fsync(6) = 0 <0.839397>
    fsync(6) = 0 <0.879706>
    fsync(6) = 0 <0.240856>
    fsync(6) = 0 <0.006497>
    fsync(6) = 0 <0.207197>
    fsync(4) = 0 <0.318396>
    fsync(4) = 0 <0.044499>
    fsync(4) = 0 <0.088381>
    fsync(6) = 0 <0.001057>
    fsync(9) = 0 <0.245389>
    fsync(7) = 0 <0.042728>
    fsync(7) = 0 <1.148262>
    fsync(6) = 0 <0.200707>
    fsync(6) = 0 <0.045259>
    fsync(6) = 0 <0.111846>

    that's all quite usable. Stuttering, yes, but never anything feeling rally
    bad, or like something died.

    This is with data=ordered on the same kernel:

    fsync(5) = 0 <0.000949>
    fsync(8) = 0 <19.674681>
    fsync(8) = 0 <1.169357>
    fsync(8) = 0 <17.994631>
    fsync(8) = 0 <5.711143>
    fsync(8) = 0 <4.759515>
    fsync(4) = 0 <17.283171>
    fsync(4) = 0 <4.371930>
    fsync(4) = 0 <0.008327>
    fsync(8) = 0 <0.000636>
    fsync(11) = 0 <9.802027>
    fsync(9) = 0 <14.109262>
    fsync(9) = 0 <4.081919>
    fsync(8) = 0 <0.000490>
    fsync(8) = 0 <0.001588>
    fsync(11) = 0 <18.822826>
    fsync(9) = 0 <3.917717>
    fsync(9) = 0 <0.001035>
    fsync(8) = 0 <0.000138>
    fsync(9) = 0 <17.466156>

    where basically each 'sync' on the big file triggers that 15-20s total
    failure. I do wonder if it's actually gotten _worse_ for the data=ordered
    case, but at the same time it does make a pretty compelling argument for
    switching the defaults around.

    Linus


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